GB549186A - Improvement in radio measuring systems - Google Patents

Abstract

549,186. Wireless receiving apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 30, 1941; No. 13987. Convention date, Oct. 31, 1940. [Class 40 (v)] In a measuring system using a receiver in collaboration with a reference oscillator, a discriminator is used to keep the frequencies of the oscillator and receiver in agreement. Fig. 1 shows an arrangement for measuring the field strength of a transmitter. The receiver comprises a loop antenna 5, radio-frequency amplifier 7, mixer 9, I.F. amplifier 13, calibrated attenuator 21 and discriminator 15 the output from which is metered at 29 and may be heard in telephones 31 to assist in identifying the transmitter under test. The output of a reference oscillator 23 is fed to a loop antenna 27 coupled to loop 5 and in order to synchronize the oscillator and receiver, a voltage from the discriminator 15 can be fed through switch 35 to a reactance valve 25 controlling the oscillator frequency. The discriminator voltage may also be fed through switch 33 to a reactance valve 17 controlling the frequency of the receiver oscillator 11. To make a test the receiver is tuned to the transmitter and the attenuator 21 is adjusted to give a convenient reading on 29. The oscillator 23 is switched on to give a much larger signal and the attenuator is adjusted to give the same meter reading. At this attenuator setting, the signal from the transmitter can be disregarded and from the available data, the transmitter strength can be calculated. Fig. 2 shows an arrangement for testing a receiver 39 by applying signals from an oscillator through a calibrated attenuator, the oscillator frequency being synchronized with the receiver by a voltage from the discriminator 37 fed through switch 49 to a reactance valve 41 controlling the oscillator frequency. A further modification is described (Fig. 3, not shown) for testing a receiver which is not provided with a discriminator. The oscillator is provided with a discriminator having leads for connection to the I.F. output of the receiver.